question about compression testing

i did my first compression test on my 79 puch 2hp and it got up to about 120. when i stopped pedaling i noticed that the pressure started to diminish slowly. is this normal or does this indicate a problem??

mopeddave

Re: question about compression testing

Jason Luther /

when you stop, you arent getting an actual reading. unless you stop at exactly tdc. when you pedel the piston is going up and down hundereds of times, and the reading on the gauge is the average of all of the compression strokes. so i would say no, nothing is wrong. although 120 is kind of low, especially for the 2 hp. but if everything runs fine, than it is fine. -jason

Re: question about compression testing

how would i know if my moped has too little compression? what are some signs or symptoms of the compression being low??

mopeddave

Re: question about compression testing

well if the gauge says its low, then its probably low,

but your bike may not run as fast or zippy as it could with higher compression

i would suggest removing some gaskets from the cylinder, i've seen up to five of the thin aluminum head gaskets used in puch engines regardless of the hp, if you take a couple out and maybe get a new base gasket and make sure everything is sealed up tight you should probably get a little bit more compression, just make sure your piston doesn't hit the spark plug

Re: question about compression testing

Don Pflueger /

your gauge is leaking. your test is not accurate. you need a new gauge.

Re: question about compression testing

Steamboat Aka J. R. Stevens /

Idon't know the type of guage you are using but mine screws into the spark plug hole and displays the highest pressure reached. This reading will remain until I press a release valve on the guage. I think your guage is just leaking down.jim

Re: question about compression testing

yeah i think the needle should stay at the number it reads until you release the pressure,

Re: question about compression testing

Don Pflueger /

i think so too. and if the gauge is leaking, he cant be getting an accurate reading. it may be close. all 3 of my gauges record the highest pressure attained. ive never seen one the dont. it doesnt matter where the piston stops.

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